1. Field of the Invention
The present invention relates to novel, useful bis(2-aminophenylthioalkyl)terephthalates and hardeners for polyurethane elastomer thereof.
2. Description of the Prior Arts
Heretofore, aromatic diamines have been used as hardeners in a preparation of a polyurethane elastomer because high mechanical characteristics are imparted by urea group or biuret group formed by a reaction of isocyanate group of a prepolymer with amino group of an aromatic diamine. A special expensive prepolymer such as 1,5-naphthalenediisocyanate should be used in the case of a diol type hardener. On the other hand, a polyurethane elastomer having excellent mechanical property can be obtained even though a prepolymer having isocyanate group which is industrially available, is used in the case of the aromatic diamine. Therefore, various aromatic diamine type hardeners have been proposed. Various conditions are, however, considered for the hardener to obtain a desired aromatic diamine type hardener.
The important factors required for the hardeners are as follows.
Firstly, it should be low melting point solid or liquid from the viewpoint of processability, labour hygiene and energy saving.
Secondly, a pot life as the time from mixing a hardener with a mixture of polyisocyanate and polyol or a prepolymer having the terminal isocyanate group to non-flowing the mixture for casting, is suitable.
Thirdly, a set time as the demoldable time from molding the mixture to demolding the casted product from the viewpoint of processability especially efficiency is suitable.
Fourthly, the object hardener is easily produced and it is stable.
Fifthly, the resulting polyurethane elastomer has excellent physical property.
However, these requirements are contradictory for example, if the short set time is required, the pot life is shortened to cause a trouble in the processing. Accordingly, it is difficult to obtain a hardener having satisfactory and balanced characteristics.
For example, when 1,2-bis(2-aminophenylthio)ethane is used as a hardener, a polyurethane elastomer having relatively improved mechanical characteristics can be obtained, but a pot life is too short to give a desired processability. This compound can not be a hardener having balanced characteristics.
The inventors have studied syntheses of various compounds for finding hardeners having satisfactory characteristics for polyurethane elastomers.